Se by Sulfur: A Density Functional Theory Study*

Silver selenide is known to possess optical response in the range that covers medium to long wavelengths. The methods of finetuning the band gap include its alloying with sulfur resulting in Ag₂Se_1-xS_x structures. In this work, the band-structure analysis of crystalline Ag₂Se with and without substitutional sulfur atoms is performed using density functional theory. The band structures of Ag₂Se_1-xS_x are computed using different theory levels, and the results are discussed and compared with experimental data. The atomic structures of bulk crystalline Ag₂Se with one to three selenium atoms substituted by sulfur are studied and the effects of substitutions on band structure specifics is discussed in the context of structural and chemical modifications taking place in these systems. The studies of strain-induced evolution of the Ag₂Se band structures for samples with and without substitutional sulfur atoms are performed to unravel the combined effects of strain and sulfur on electronic structure of Ag₂Se_1-xS_x. All the calculations have been performed for an Ag₂Se unit cell and supercells of varied sizes. The implications of the obtained results for Ag₂Se-based photodetectors will be discussed.